1. Field of the Invention
The present invention relates to a wafer which is used for evaluating the uniformity of a furnace temperature, concentration of gases, or the like, for removing contaminants, and for determining various processing conditions in processing stages of thermal diffusion, thermal oxidation, and vapor phase epitaxy or the like to a silicon wafer (hereinafter, "dummy wafer") when an integrated circuit or the like is manufactured.
2. Description of the Related Art
In the manufacturing process of a semiconductor device such as LSI, it is important to carry out a stage of oxidizing the surface of a wafer, a stage of diffusing a doping element such as phosphorus or boron within silicon, a stage of forming various coatings on the surface of the wafer due to CVD (chemical vapor deposition) or PVD (physical vapor deposition). In order to improve the yield of a product and to manufacture a device of higher integrity, it is important to maintain the processing conditions constant in these stages.
In the above-described stages, in general, a batch processing is used in which a boat in which 100 pieces or more of wafers are attached is placed in a reactor having a heater and the wafers are subjected to processings. However, in such processing, there are drawbacks in that the temperature and the concentration of raw material gas vary in accordance with the position of the wafer within the reactor. For this reason, dummy wafers, which are not used as product wafers, are disposed at places within the reactor where the processing conditions, such as the temperature within the reactor and the concentration of the raw material gas may be different from those at the other places within the reactor. The uniformity of the processing conditions is assessed by determining whether the thicknesses and components of thin films, which are superposed one on top of another at each of the dummy wafers, are the same. Further, the dummy wafers are used for studying the processing conditions of plasma in an etching device and for removing particles generated within the device. The dummy wafers used for these purposes are repeatedly used at high temperatures, and are repeatedly processed by acid so as to remove the coating formed on the dummy wafers and thereby enable the repetition of use thereof.
Conventionally, silicon or quartz which is the same as the material of an ordinary product wafer is used as the material of a dummy wafer. However, in a case in which a dummy wafer formed with silicon is used, since the heat resistance of silicon is not good, the configuration of the dummy wafer is easily changed over time, and since the acid resistance of silicon is low, the surface of the dummy wafer becomes rough due to dissolution by acid and particles are easily generated. Accordingly, the life of the dummy wafer is short. On the other hand, in case of quartz, since the heat resistance and acid resistance thereof are not sufficient and quartz is not conductive, the dummy wafer cannot be used for etching processing or the like. Therefore, instead of silicon and quartz, a carbon material of excellent heat resistance and a ceramics material of excellent acid resistance are desirable as the material of dummy wafers. Above all, since the components are harmless to a semiconductor device serving as a product, a silicon carbide sintered body is the most desirable.
However, because it is difficult to sinter silicon carbide, a small amount of boron carbide, alumina, or the like is generally added to the silicon carbide as an additive for facilitating the sintering. Since these additives become impurities, a conventional silicon carbide is inappropriate as a material of the aforementioned dummy wafer.
Accordingly, a silicon carbide sintering method and a sintered body which does not use the aforementioned harmful additive are desired. For example, i) a method of manufacturing a sintered body with fine powder formed through vapor phase epitaxy employing gas or a solution including silicon and carbon as a material and by using the formed powder as a material; and ii) a method of manufacturing directly a plate-shaped molded body (sintered body) through vapor phase epitaxy employing gas or a solution including silicon and carbon as a material are proposed.
However, in these methods, there are drawbacks in that the productivity is very poor and the cost is high. Further, the above-described Method i) has a drawback in that the powder is too fine and particles are easily generated even after the powder is sintered. Method ii) has a drawback in that it is difficult to manufacture a thick molded body.